The present invention relates to an electric universal motor according to the preamble of claim 1. In the case of a known electric drive motor of this type (DE-OS 31 49 106) the stator, which is formed by a permanent magnet, is surrounded by an annular sheet-steel strip forming a magnetic short-circuit, the two sides of the strip being arranged axially adjacent and connected to bearing supports. The bearing supports have the form of brackets and accommodate each one shaft bearing for the rotor shaft. One of the shaft bearings is designed as a roller bearing which is held directly in a pot-shaped recess of the bearing support and projects outwardly therefrom by a predetermined amount. It is thereby possible to use this bearing element, i.e. in the particular case the outer ring of the roller bearing, which necessarily extends absolutely centrically to the bearing element, for receiving and centering another assembly arranged on the motor, such as a gear box. As regards the electric wiring possibilities, no details are provided; but complicated arrangements are certainly not required given the fact that the stator consists of a permanent magnet.
It has been further known (U.S. Pat. No. 4,613,781) in connection with an electric motor to equip one side of the motor with an end cap assembly comprising a plastic component with a plurality of strip-like metallic lines embedded in its interior for establishing electric connections between the motor components and brush holders. To this end, each electric line which is intended to make contact with a brush holder is wound about a base portion of the brush holder, each brush holder being equipped for this purpose with lateral flanges provided on its base.
In addition, the individual brush holders are designed in such a manner that the lateral wall is bent off in the form of a loop and lengthened so that it reaches below the respective carbon brush in the brush holder, in the manner of a hook, for the purpose of holding the brush at a certain distance relative to the collector ring of the armature during the assembly operation. Thereafter, i.e. after completion of the assembly operation, the hook is pressed outwardly whereby the carbon brush is released so that contact can be made between the brush and the collector of the electric motor.
It has been further known in connection with an assembly for an electric motor (DE-GM G 85 20 258.4) to provide a plate consisting of an insulating material and carrying a circuit arrangement with a central opening for the collector of an electric motor, and to design the frame parts, which are arranged on the plate opposite each other and intended for holding brushes that can be connected to the circuit arrangement, in such a manner that resiliently biassed extensions of the springs of spring-loaded mounting means arranged laterally beside the frame parts extend into the frame parts. The springs are wound upon the spring-loaded mounting means in the form of a coil. At least one portion of the electric circuit arrangement is embedded in the plastic carrier plate.
This method of embedding at least the essential components of the wiring required for the operation of an electric motor has been known also from DE-OS 36 04 675. In this case, an insulating component is used for embedding the essential parts of the conductor path and for supporting at the same time other components necessary for operating the motor, such as brush rockers, which are likewise integrated in the same component. The component is designed in the form of a plate with a central bore enabling the collector of the electric motor to be passed through the plate.
In the case of another electric motor of known design (European Patent Application No. 0 235 443), an annular carrier plate carries a plurality of electric components making contacts with electric lines embedded in the carrier plate due to the fact that the electric lines are partially released by the carrier plate for contact-making purposes. Brush holders, which are likewise mounted on the carrier plate, are provided with lateral extensions which are snapped over free conductor areas, in the manner of a snap-on connection, so that a safe form-locking connection is obtained between the lines inside the carrier plate and the housings of the brush holders. But the assembly input required for mounting a plurality of components on the carrier plate, including separate, wound biassing springs for the brushes and their carrier pins, is already very considerable; and in addition, parts of the electric lines which are embedded in the carrier plate extend from the latter in the axial direction in order to establish the contact to the another part, for example the stator.
It has further been known, in connection with an electric motor for a smaller electric tool, to design a cup-shaped bearing support in such a manner that it forms sort of a partial housing for the stator accommodated therein, with the rotor being arranged to rotate freely inside the stator. The rotor shaft is seated on the side of the cup-shaped bearing support, in a roller-bearing formed by the bearing support. In addition, the bearing support is equipped with switching-on and cut-off means, field plugs and a suppression capacitor. A contact grid arranged on the bearing support is designed in the form of a punched grid for the selective connection of reactance coils, change-over switches, diodes and resistors. The punched grid is connected to the side of circuit arrangement facing the rotor. In addition, a switching ring is provided the rotation of which enables different contacts to be made, for example for reversing the sense of rotation or reducing the speed (European Patent Application No. 0 224 054).
It has been further known in this connection (European Patent Application No. 0 224 053), to arrange the plane punched grid on one side of a carbon holder plate, with the carbon brushes being arranged on the other side of the carbon holder plate. The connection contacts for the field windings are obtained in this manner by connection reeds which are bent off at a right angle relative to the main plane of the punched grid. The punched grid takes the form as a continuous metal strip line and is welded, bonded or connected in any other manner to the surface on the rotor side of the carbon holder plate which as such consists of a plastic material.
It is a problem of the known electric motors and/or of their components that although some simplifications can be achieved by certain individual features, the resulting structures are still extremely complex as regards the number of individual components, the operation of fitting them together, and the assembly of the electric motor, and this in particular if one considers that such an electric motor should also be provided with means enabling it to be switched on and off, and, above all, enabling its sense of rotation to be reversed. However, it is exactly the reversal of the sense of rotation which is connected with considerable circuitry input so that considerable problems have to be overcome in this connection, but also as regards the support of the brushes and the establishment of contacts between the latter and other circuit components, and quite generally in connection with the whole basic structure and design of the electric motors, which problems stand in the way of a substantially automatic assembly and low-cost production of electric motors.
Now, it is the object of the present invention to provide an electric universal motor which requires only a small number of individual components, is capable of giving high continuous performance, meets all demands regarding the electric wiring possibilities, including the connection of switch-on, cut-off and change-over switches, and which is still designed in such a manner that it can be produced on automatic production lines, without any sacrifices regarding stability and, above all, the exact centering of the rotor relative to the stator surrounding it or the latter's pole shoes.